Hot deformation behavior and deformation mechanism of two TiAl-Mo alloys during hot compression

Two TiAl alloys with different Mo contents (Ti-44Al-4Nb-1.0Mo-0.1B-0.01Y, and Ti-44Al-4Nb-1.5Mo-0.1B-0.01Y, referred to LM and HM alloys, respectively) are prepared, and their hot deformation behaviors are characterized via hot compression tests. The results show that the addition of Mo not only refines the grain size of the TiAl alloy but also improves the amount of β phase in TiAl alloy. The hot processing map developed at a true strain of 0.6 shows that the workability of the alloys decreases with increasing the strain rate and decreasing the temperature. The LM and HM alloys have a similar distribution of instability region in processing map, but they do have different instability parameter values, the difference of which is attributed to the cracking in the LM alloy, as well as the “lubrication effect” of β phase in HM alloy. During hot deformation process, the deformation mechanism in LM alloy relies on the dislocation slip of γ and α phase, while in HM alloy there is dislocation slip of β and γ phase, as well as twinning in the γ phase.